1. Field of the Invention
The present invention relates to a magnetic recording media, a magnetic recording system and a method of forming them.
2. Discussion of the Background
Recently, in a magnetic recording media, as a recording density is more enhanced, a more stable magnetization in recording against a thermal fluctuation is required. Therefore, there is a tendency that the uniaxial magnetic anisotropy constant (Ku) of a magnetic material is increasing, which is used as a material of a magnetic layer responsible for recording. A large recording magnetic field is required so as to carry out recording on the magnetic layer having a large Ku. Consequently, a study has been conducted as to a write head which generates the recording magnetic field, from both structural and material viewpoints. In the meantime, there has been suggested a perpendicular recording method where two-layer perpendicular media provided with a soft magnetic under layer and a single magnetic polar head are combined.
In the method above, a main pole of the write head, the soft magnetic under layer, and an auxiliary pole of the write head form a closed magnetic circuit, and then larger amount of magnetic flux passes through the magnetic layer, comparing to a conventional in-plane recording. Therefore, the recording method using the two-layer perpendicular media has a higher efficiency in utilizing of the recording magnetic field, comparing to the in-plane recording method which carries out recording by use of only in-plane substances in the recording magnetic field. Therefore, it has been considered that according to the recording method using the two-layer perpendicular media, recording onto recording media with a higher Ku is possible, than the case where the in-plane recording method is used.
However, since the magnetic field intensity applied on the media does not go over the intensity generated in the main pole, a saturation flux density (Bs) of the main pole material is equal to an upper limit of the recording magnetic field intensity. The saturation flux density has a physical restriction determined by a material, and consequently, the upper limit of the recording magnetic field applied on the media is determined based on the value of the restriction. In order to increase the saturation flux density, various materials have been developed, but it is impossible to increase the density infinitely.
Further, it is known that a material with a high saturation flux density, currently under development, generally has a problem in corrosion resistance. Therefore, as the uniaxial-magnetic anisotropy constant (Ku) of a recording media increases, it is conceivable that recording, on such recording media may become difficult in the future, even if the perpendicular recording method is used.
Further, as a form of the recording media suitable for high recording density, there is known a method, so-called patterned media, where a magnetically isolated magnetic particle is arranged regularly and recording is performed by corresponding one bit to one particle; This method is disclosed, for example, by Japanese Patent Application Laid-Open Publication No. Hei 1-155897, No. Hei 2-100308, and U.S. Pat. No. 5,587,223 (Hereinafter, referred to as Patent Documents 1, 2 and 3, respectively). In this method, noises due to instability in the magnetic state within the bit transition region are not generated, and it is possible to make 1 bit as small as possible until the limit of the thermal fluctuation. Therefore, it is conceivable that this method is advantageous to the high-density magnetic recording.
In the case of the patterned media, it is possible to make equal the size of the magnetic particle forming the bit and the size of one bit. Therefore, it is possible to achieve a larger volume (v) for a magnetization reversal unit, than that of continuous media where one bit is made of a large number of grains. In other words, it is conceivable that if compared in a same recording density, Ku is allowed to be smaller on the patterned media than a conventional continuous media.
However, even though the patterned media recording method is used, if Ku of the magnetic layer increases with the enhancement of recording density, it is conceivable that recording may become difficult, as in the case where the continuous media is used.
[Patent Document 1]
    Japanese Patent Application No. Hei 1-155897[Patent Document 2]    Japanese Patent Application No. Hei 2-100308[Patent Document 3]    U.S. Pat. No. 5,587,223[Patent Document 4]    International Application No. PCT/JP01/07211[Patent Document 5]    Japanese Patent Application Laid-Open Publication No. 2001-110001[Patent Document 6]    Japanese Patent Application Laid-Open Publication No. 2001-256605[Patent Document 7]    Japanese Patent Application Laid-Open Publication No. 2002-92821[Non-Patent Document 1]    R. Wood, IEEE Transaction on Magnetics Vol. 36 (2000), No. 1, pp. 36